The prevention of oxidation of various organic materials is obviously of primary industrial concern and therefore antioxidants are used in or added to a wide variety of commercial products such as synthetic polymers of the type indicated supra, oils, plastics, etc., which are normally subject to oxidative deterioration.
The mechanism of the action of a hindered phenol compound as an antioxidant has not been definitely established. It is believed, however, that the hindered phenol acts as a chain-stopper for the free radical chain mechanism of oxidation either by donation of hydrogen or donation of an electron to a free radical involved in the oxidation process or the combination of a free radical with the aromatic ring of the antioxidant either by direct addition or by .pi. -complex formation.
It is generally believed that free radicals, necessary for the polymerization of vinyl and related monomers, are trapped by antioxidants such as hindered phenols. For this reason, polymerizations of vinyl monomers carrying a phenolic group or a hindered phenolic group were carried out by a series of steps which included (a) esterification of the phenol group, (b) free radical polymerization of the vinyl group and (c) hydrolysis of the ester group to obtain the desired polymeric antioxidant. This procedure is illustrated by S. N. Ushakov et al., USSR Pat. No. 149,888 as follows: ##SPC1##
And by G. Manecke + G. Bourwieg, Makromolekare Chemie, 99 (1966) 175-185 as follows: ##SPC2##
It has now been found that monomers containing hindered phenolic groups can be directly polymerized by free alkyl- or aryl- radicals to produce the desired polymeric antioxidants of the present invention.